In defense of the 1.5C climate change threshold

The Earth today is more than 1 degree centigrade hotter than it was in pre-industrial times, and the terrible symptoms of its fever are already showing. This year alone, back-to-back hurricanes have devastated Caribbean islands, monsoon flooding has displaced tens of millions in South Asia, and fires have raged on nearly every continent. Pulling the planet back from the brink could not be more urgent.

Those of us who live on the front lines of climate change – on archipelagos, small islands, coastal lowlands, and rapidly desertifying plains – can’t afford to wait and see what another degree of warming will bring. Already, far too many lives and livelihoods are being lost.

People are being uprooted, and vital resources are becoming increasingly scarce, while those suffering the most severe consequences of climate change are also among those who have done the least to cause it.

That is why the Philippines used its chairmanship of the Climate Vulnerable Forum (CVF) – an alliance of the 48 countries that stand to bear the brunt of climate change – to fight to ensure that the 2015 Paris climate agreement aimed explicitly to cap global warming at 1.5C above pre-industrial levels. For us, 1.5C isn’t merely a symbolic or “aspirational” number to be plugged into international agreements; it is an existential limit. If global temperatures rise above that level, the places we call home – and many other homes on this planet – will become uninhabitable or even disappear completely.

When we first introduced the 1.5C target back in 2009, we met substantial resistance. Climate-change deniers – those who refuse to believe the science of human-induced global warming – continue to dismiss any such effort to stem the rise in the planet’s temperature as futile and unnecessary. But even well-meaning climate advocates and policymakers often opposed the 1.5C target, arguing that, according to the science, humans had already emitted enough greenhouse gases to make meeting that goal virtually impossible.

Yet, on this front, the science is not as clear-cut as it might have seemed. According to a recent paper published in ‘Nature’, the world’s remaining “carbon budget” – the amount of carbon-dioxide equivalents we can emit before breaching the 1.5C threshold – is somewhat larger than was previously thought.

This finding is no

reason

for

complacency,

as some commentators (not scientists) seem to think. It does not mean that previous climate models were excessively alarmist, or that we can take a more relaxed approach to reining in global warming. Instead, the paper should inspire – and, indeed, calls for – more immediate, deliberate, and aggressive action to ensure that greenhouse-gas emissions peak within a few years and net-zero emissions are achieved by midcentury.

What would such action look like? Global emissions would need to be reduced by 4-6% every year, until they reached zero.

Meanwhile, forest and agricultural lands would have to be restored, so that they could capture and sequester greater amounts of carbon dioxide. Fully decarbonising our energy and transportation systems in four decades will require a herculean effort, but it is not impossible.

Beyond their environmental consequences, such efforts would generate major economic gains, boosting the middle class in developed countries and pulling hundreds of millions out of poverty in the developing world, including by fuelling job creation. The energy transition will lead to massive efficiency savings, while improving the resilience of infrastructure, supply chains, and urban services in developing countries, particularly those in vulnerable regions.

According to a report published last year by the United Nations Development Programme, maintaining the 1.5C threshold and creating a low-carbon economy would add as much as $12 trln to global GDP, compared to a scenario in which the world sticks to current policies and emissions-